SO the guy at the fish store said that a good tank mate for my bettas that would clean the bottom of the tank would be the small catfish. He said they like to be in pairs but do just fine on their own and it would be fine getting one for each section of my 10 gallon tank divided three ways and they would clean the gravel much better than ghost shrimp would. What do you think?

He also said it'd be okay if I wanted to put one guppy or one platy in there with each betta but I wasn't too sure about that. (Not in addition to the catfish)

Thats what I thought...I just wanted to make sure. I do have an ADF in one section and he's getting along fine with the betta. I had another one who was getting along fine but he kept getting into the divider with the betta with no tank mates who was more agressive and would nip at him and he died after a week. I plan on getting ghost shrimp though.

I agree. Some shrimp would do just fine.. But Ghst shrimp tend to be aggressive towards fish if they dont feel comfortable in the tank.. So you should get more then 1 for each section and some hiding places and some plants will lower the aggression towards the Betta...
I have actually had a ghost shrimp shread one of my male Bettas fins before.. Of course thats when I didnt know much about them.. But the plants and hiding places will help. :]